The folder tree is where your jobs are stored. Each job can be in the main folder or they can be stored in sub folders. The preference for how you store jobs is really up to you.
In this example, there is a folder called BASIC_NESTING_JOBS:
Selecting the BASIC_NESTING_JOBS folder opens the tree further to show the jobs that have been located there.
There could have been even more folders in this folder if the jobs needed to be separated further.